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United States Patent |
5,204,210
|
Jansen
,   et al.
|
April 20, 1993
|
Method for the direct patterning of diamond films
Abstract
A method of forming a patterned, poly-crystalline diamond film on a
substrate is disclosed. First, a photoresist layer is applied to a
substrate. A diamond powder layer is formed on the photoresist layer
either through spray-coating, dip-coating, spin-coating using a
diamond-powder suspension, and the like. The photoresist layer is exposed
to electromagnetic radiation through a mask either before or after the
diamond powder layer is applied. Then, the photoresist layer is developed,
after which the substrate is heated causing the photoresist layer to
carbonize. The substrate is exposed to a mixture of hydrogen-containing
and carbon-containing gases which are decomposed in a processing
apparatus. Hydrogen in this gas mixture etches away at the carbonized
photoresist layer leaving behind the patterned diamond powder layer.
Carbon in these carbon-containing gases combines with the diamond
particles in the diamond powder layer to form diamond structures on the
substrate.
Inventors:
|
Jansen; Frank (Webster, NY);
Machonkin; Mary A. (Webster, NY)
|
Assignee:
|
Xerox Corporation (Stamford, CT)
|
Appl. No.:
|
624031 |
Filed:
|
December 7, 1990 |
Current U.S. Class: |
430/198; 427/228; 427/249.9; 427/402; 427/558; 430/330; 430/350 |
Intern'l Class: |
G03C 011/00; B05D 003/02 |
Field of Search: |
430/330,325,198,350
427/38,99,249,255.2,259,402,228
|
References Cited
U.S. Patent Documents
2900255 | Aug., 1959 | Charlton | 430/198.
|
3317319 | May., 1967 | Mayaud | 430/330.
|
3443944 | May., 1969 | Wise | 430/198.
|
3481733 | Dec., 1969 | Evans | 430/198.
|
3637385 | Jan., 1972 | Hayes et al. | 430/330.
|
3754912 | Aug., 1973 | Jones et al. | 430/330.
|
3958996 | May., 1976 | Inskip | 430/198.
|
3982941 | Sep., 1976 | Inskip | 430/198.
|
4104441 | Aug., 1978 | Fedoseev et al. | 427/249.
|
4410611 | Oct., 1983 | MacIver et al. | 427/38.
|
4529860 | Jul., 1985 | Robb | 430/330.
|
4554208 | Nov., 1985 | MacIver et al. | 427/38.
|
4613560 | Sep., 1986 | Dueber et al. | 430/198.
|
4618505 | Oct., 1986 | MacIver et al. | 427/38.
|
5006203 | Apr., 1991 | Purdes | 427/38.
|
Foreign Patent Documents |
1-162757 | Jun., 1989 | JP | 427/249.
|
Other References
J. C. Angus et al., "Growth of Diamond Seed Crystals by Vapor Deposition",
vol. 39, May 1968, 2915-2922.
|
Primary Examiner: Bowers, Jr.; Charles L.
Assistant Examiner: Angebranndt; Martin
Attorney, Agent or Firm: Kenyon & Kenyon
Claims
What is claimed is:
1. A method of forming a patterned, poly-crystalline diamond film on a
substrate, comprising:
applying to a substrate a photoresist layer;
applying to said photoresist layer a diamond powder layer, said diamond
powder layer including diamond particles;
exposing said photoresist layer and said diamond powder layer to
electromagnetic radiation through a mask;
developing said photoresist layer sufficiently to form a developed
photoresist layer;
heating the substrate, developed photoresist layer, and diamond powder
layer in a processing apparatus, said heating step causing said developed
photoresist layer to carbonize;
introducing a mixture of gases into said apparatus, said mixture of gases
including carbon-containing and hydrogen-containing gases; and
decomposing said mixture of gases in said apparatus, whereby hydrogen in
said hydrogen-containing gases remove said carbonized photoresist layer,
and whereby carbon in said carbon-containing gases combines with said
diamond particles forming diamond structures on said substrate.
2. The method of claim wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by spin coating.
3. The method of claim 1 wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by dip coating.
4. The method of claim 1 wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by spray
coating.
5. The method of claim 1 wherein in said exposing step, said
electromagnetic radiation is Ultra-Violet light.
6. The method of claim 1 wherein in said applying a diamond powder layer
step, diamond particles are applied to the substrate in an amount of from
about one to ten particles per square micron with an average particle
diameter of from about 0.01 to about 0.4 microns.
7. The method of claim wherein said processing apparatus is a deposition
chamber.
8. The method of claim 1 wherein said hydrogen-containing gas is diatomic
hydrogen.
9. The method of claim 1 wherein in said heating step, the substrate is
heated to a temperature from about 400.degree. to about 900.degree. C.
10. The method of claim 1 wherein the thickness of said diamond structures
is from about 0.1 to about 1000 microns.
11. The method of claim 1 wherein in said introducing a mixture step, said
mixture of gases includes carbon-containing gases in a concentration from
about 0.1 to about 3 percent by volume.
12. A method of forming a patterned, poly-crystalline diamond film on a
substrate, comprising:
applying to a substrate a photoresist layer;
exposing said photoresist layer to electromagnetic radiation through a
mask;
applying to said photoresist layer a diamond powder layer, said diamond
powder layer including diamond particles;
developing said photoresist layer sufficiently to form a developed
photoresist layer;
heating the substrate, developed photoresist layer, and diamond powder
layer in a processing apparatus, said heating step causing said developed
photoresist layer to carbonize;
introducing a mixture of gases into said apparatus, said mixture of gases
including carbon-containing and hydrogen-containing gases; and
decomposing said mixture of gases in said apparatus, whereby said
hydrogen-containing gases remove said carbonized photoresist layer, and
whereby carbon in said carbon-containing gases combines with said diamond
particles forming diamond structures on said substrate.
13. The method of claim 12 wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by spin coating.
14. The method of claim 12 wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by dip coating.
15. The method of claim 12 wherein in said applying a diamond powder layer
step, diamond powder is applied from a suspension thereof by spray
coating.
16. The method of claim 12 wherein in said exposing step, said
electromagnetic radiation is Ultra-Violet light.
17. The method of claim 12 wherein in said applying a diamond powder layer
step, diamond particles are applied to the substrate in an amount of from
about one to ten particles per square micron with an average particle
diameter of from about 0.01 to about 0.4 microns.
18. The method of claim 12 wherein said processing apparatus is a
deposition chamber.
19. The method of claim 12 wherein said hydrogen-containing gas is diatomic
hydrogen.
20. The method of claim 12 wherein in said heating step, the substrate is
heated to a temperature from about 400.degree. to about 900.degree. C.
21. The method of claim 12 wherein the thickness of said diamond structures
is from about 0.1 to about 1000 microns.
22. A method of forming a continuous, poly-crystalline diamond film on a
substrate, comprising:
applying to a substrate a photoresist layer;
applying to said photoresist layer a diamond powder layer, said diamond
powder layer including diamond particles;
heating the substrate, photoresist layer, and diamond powder layer in a
processing apparatus, said heating step causing said photoresist layer to
carbonize;
introducing a mixture of gases into said apparatus, said mixture of gases
including carbon-containing and hydrogen-containing gases; and
decomposing said mixture of gases in said apparatus, whereby said
hydrogen-containing gases remove said carbonized photoresist layer, and
whereby carbon in said carbon-containing gases combines with said diamond
particles forming a diamond film on said substrate.
23. A method of forming a patterned, poly-crystalline diamond film on a
substrate, comprising:
applying a photoresist layer to a silicon substrate;
applying to said photoresist layer a diamond powder layer, said diamond
powder layer formed from diamond particles having an average diameter of
0.1 microns;
exposing said photoresist layer and diamond powder layer to Ultra-Violet
light through a mask;
developing said photoresist layer sufficiently to form a developed
photoresist layer;
heating the substrate, developed photoresist layer, and diamond powder
layer in a deposition chamber, said heating step causing said developed
photoresist layer to carbonize;
introducing a mixture of gases into said chamber, said mixture of gases
including a diatomic hydrogen gas and a hydrocarbon gas; and
decomposing said mixture of gases in said chamber, whereby hydrogen removes
said carbonized photoresist layer, and whereby carbon in said hydrocarbon
gas combines with said diamond particles forming diamond structures on
said substrate.
Description
BACKGROUND OF THE INVENTION
The present invention pertains to thin-film patterning, and more
particularly to the patterning of diamond film on a substrate.
Diamond thin films have a variety of uses such as razor blades, tool bits,
and surgical instruments, especially in neurosurgery, where diamond thin
films have been used in scalpels. Because of its excellent heat conduction
properties, diamond thin films have been used in heat-sink applications
such as heat conductive coatings in microelectronic components.
A number of methods have been employed for forming a diamond thin film on a
substrate in connection with the uses described above. For example, U.S.
Pat. No. 4,740,263 discloses the forming of a diamond film on a
semiconductor surface using electron assisted chemical vapor deposition
(EACVD). In this method, the semiconductor substrate is heated and
bombarded with electrons in a hydrocarbon gas to produce nucleation sites
on the substrate surface. A similar method is disclosed in U.S. Pat. Nos.
4,830,702 and 4,842,945.
In U.S. Pat. Nos. 4,844,785 and 4,919,974, a diamond film is formed by
impinging carbon particles onto a substrate at a high temperature. In U.S.
Pat. No. 4,869,923, a nitrogen compound and a carbon compound are placed
in a reaction chamber with a semiconductor substrate. The nitrogen
compound assists in adhering carbon particles to the substrate surface.
In "Ion-Beam-Assisted Etching of Diamond" by N. N. Efremow, M. W. Geis, D.
C. Flanders, G. A. Lincoln, and N. P. Economou, J. Vac. Sci. Technol. B3
(1985), there is a lengthy discussion of an unconventional method of
etching a single crystalline diamond layer with xenon and nitrogen dioxide
to make desired patterns. Although effective, this technique tends to be
cumbersome. Conventional reactive ion etching (RIE) with oxygen, also
mentioned in the paper, tends to be slow. As a further complication for
polycrystalline diamond, the etching rate differs for each energy for the
various faces of the diamond lattice.
One of the more common methods is discussed in Selective Deposition of
Diamond Films by J. L. Davidson et al. (Elec. Eng. Dept. of the Alabama
Microelectronics Science and Technology Center, Auburn Univ.). The method
of this article employs the deposition of diamond films on a "scratched"
surface of a silicon substrate. Initially, a polished silicon substrate
surface is scratched by a diamond paste. After a cleaning step, a layer of
silicon nitride is then formed on the scratched surface and patterned
using standard photolithographic processes. Then, exposed silicon is
oxidized and the remaining silicon nitride is removed, leaving areas of
scratched silicon substrate exposed. A carbon-bearing gas, such as
methane, is decomposed near the substrate in a manner which permits carbon
radicals of the gas to adhere to the scratched silicon surface, more so
than to a smooth silicon surface.
Although scratches in the silicon surface provide nucleation sites for
diamond growth, the diamond growth does not always occur. Also, after
initially scratching the silicon surface, some particles in the diamond
paste are left behind, even after cleaning, forming unwanted nucleation
sites. Small particles of any material having a high surface energy can
act as nucleation centers. This scratching method is believed to be
inadequate for optical substrates and unfeasible for microelectronic
substrates which already contain circuitry.
Patterned diamond thin films have been found to be particularly amenable to
uses in microelectronic applications. Since diamond structures have such
good heat conduction properties, patterned diamond thin films can be used
as heat sinks in microelectronic circuitry. Also, non-continuous diamond
thin films negate stress components in a semiconductor wafer arising from
differential thermal expansion and intrinsic stress.
A problem with the processes noted above is that the forming of diamond
thin films on a substrate can not often be accomplished in an economically
efficient manner. Also, it is often difficult to form diamond structures
in specific areas particularly in a microelectronic environment where
space is at a premium.
SUMMARY OF THE INVENTION
The invention relates to a method of direct patterning of diamond thin
films that overcomes the deficiencies noted above. In connection with
microelectronic circuitry, a photoresist layer is initially formed on a
substrate. After a diamond powder layer is formed on this photoresist
layer, the photoresist is exposed to electromagnetic radiation through a
mask. The photoresist layer is then developed, thus patterning the
photoresist layer and effectuating a removal of diamond powder in certain
areas. The substrate is then placed in a processing apparatus and heated,
causing it to carbonize. A mixture of hydrogen-containing and
carbon-containing gases are introduced into the processing apparatus and
decomposed. Hydrogen in this mixture reacts with the carbonized
photoresist layer to effect removal of this layer, leaving a patterned
diamond powder layer on the substrate. In this manner the decomposed gases
permit the application of diamond structures on the substrate in the
patterned areas.
In an alternate embodiment of the invention, the photoresist layer is
exposed to electromagnetic radiation before the application of the diamond
layer. The diamond layer can be applied by such methods as dip-coating,
spray-coating, or spin-coating a suspension of diamond particles. A
continuous diamond film can be formed on the substrate using the method of
the present invention by forgoing the exposing and development of the
photoresist layer.
An advantage of the present invention is that diamond thin films can be
disposed on semiconductor wafers and components without damaging the
semiconductor surface. Also, the method of the present invention is
believed to be simpler and more economical than previous diamond
deposition methods. Furthermore, the present invention is believed to
allow better control of the placement of diamond thin layers on a
substrate surface.
The above is a brief description of some deficiencies in disclosed diamond
thin film methods and advantages of the present invention. Other features,
advantages and embodiments of the invention will be apparent to those
skilled in the art from the following description, accompanying drawings
and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a-f are enlarged cross-sectional views of the formation of diamond
structures on a substrate according to an embodiment of the present
invention;
FIGS. 2a-f are enlarged cross-sectional views of the formation of diamond
structures on a substrate according to another embodiment of the present
invention; and
FIG. 3 is a scanning electron micrograph of a diamond film pattern on a
substrate constructed according to the present invention.
DETAILED DESCRIPTION
In the drawings, like reference numerals have been used throughout to
designate identical elements. Referring to FIG. 1, a method of the present
invention is shown. Substrate 1 as shown in FIG. 1a, can be formed from
standard semiconductor material such as silicon, germanium,
gallium-arsenide, and the like. Substrate 1 can also be formed from steel
or other materials which are more suitable for instrument applications
such as surgical devices or razor blades. Since the substrate 1 can have a
variety of forms and sizes, the thickness dimensions of the substrate are
not important. Although substrate is described in connection with planar
objects such as a semiconductive wafer, the substrate can be
three-dimensional objects such as a tool bit or an optical device. In the
present embodiment, substrate 1 is formed from silicon in a known method
familiar to those in the semiconductor arts. Rather than abrading the
surface of the substrate as in previous methods, the surface is kept as
smooth as possible as in standard photolithographic processes.
Referring to FIG. 1b, the substrate 1 is then coated with any of a variety
of positive or negative photoresists. The photoresist layer 3 can be, for
example, positive KTI photoresist (820, 27cs), which is generally
available. Photoresist layer 3, is formed on substrate 1 by pouring the
photoresist onto substrate until the latter is completely covered, then
spinning the substrate in a spin-coater at a high speed, such as 5,000
R.P.M., for approximately one minute. The substrate 1 and photoresist
layer 3 combination is then baked at 90.degree. C. for approximately 15
minutes. The thickness of the photoresist layer 3 can be from 0.5 to 10
microns, and preferably between 1 and 2 microns.
Referring to FIG. 1c, a diamond powder layer 5 is disposed onto the
photoresist layer 3. There are several different possible methods for
forming the diamond powder layer 5. A crude method would be to sprinkle
dry diamond particles onto the photoresist layer 3. In this method,
diamond particles can be sifted through a fine wire mesh. A more elaborate
method is the use of electrostatic development. These dry methods may
result in the clumping of particles together and give unsatisfactory
results. Alternatively, diamond particles can be suspended in a solution,
such as an alcohol. In this embodiment, diamond particles should have an
average diameter of 0.01 to 0.4 microns. For instance, 0.1 micron
particles can be obtained in bulk having a diameter ranging from 0.05 to
0.25 microns. A suspension can be made by taking 8 mg of 0.1 micron
diamond particles and adding 4 ml isopropanol. This solution is then
agitated using a microsonic stylus for approximately two minutes. The
solution is then added to the substrate immediately to prevent settling of
the suspension. The suspension can be applied to the photoresist layer
using several processes. The suspension can be applied by dipping the
substrate 1 and photoresist layer 3 combination into the suspension. This
procedure is more commonly referred to as dip-coating. Secondly, the
suspension can be sprayed directly onto the photoresist layer 3.
Dip-coating and spray-coating are more appropriate when the substrate is
not flat as it invariably is in such processes as integrated circuit chip
fabrication. A third process for forming the diamond powder layer 5, is by
spin-coating. The diamond powder suspension is gently poured over the
substrate 1 and photoresist layer 3 combination. The substrate 1 is then
spun at a fast rate, for example 3,000 R.P.M., for approximately 30
seconds in a spin-coater. Spin-coaters are well-known in the art and
common in most photolithographic processes. Because the substrate 1 is
spun rather quickly, the isopropanol in the diamond powder suspension
evaporates leaving the diamond powder layer 5. The diamond particles tend
to be evenly disposed on the photoresist layer 3. In this embodiment, the
distribution of diamond particles tends to be one to ten particles per
square micron. Also, the diamond particles tend to adhere well to the
surface of the photoresist layer 3. The entire structure is then soft
baked at 90.degree. C. for approximately 15 minutes.
Referring to FIG. 1d, the forming of specific structures in the photoresist
layer 3 and diamond powder layer 5 is shown. A mask 7 or similar device is
placed above the diamond powder layer 5. The mask 7 selectively allows
electromagnetic radiation, such as visible light, pass through in certain
areas, as is well known in the art. The mask 7 is exposed to Ultra-Violet
(UV) light for an appropriate amount of time. The diamond powder layer 5
and the photoresist layer are, thus, partially exposed to the UV light.
The photoresist layer 3 is then developed in any of a variety of well
known methods. For example, the substrate 1 can be spun while applying KTI
809 3:1 developer for 24 seconds from a nozzle (not shown) directly over
the diamond powder layer 5 and photoresist layer 3. The entire structure
can then be rinsed with distilled water from a nozzle (not shown) directly
over the diamond powder layer 5 and photoresist layer 3. Diamond particles
that were present on top of those parts of the photoresist layer 3 that
were exposed to the UV light are removed during this lift-off process.
Referring to FIG. 1e, the removal of the patterned photoresist layer 3 is
shown. After the photoresist layer has been developed, the entire
structure is placed into a processing apparatus, such as a deposition
chamber, and heated to a high temperature, such as 400.degree.-900.degree.
C. This heating step has the effect of carbonizing the photoresist layer
3. Then, during the deposition of diamond, the deposition chamber is
subjected to a vacuum, preferably 1 mTorr to 10 mTorr. Hydrogen-containing
gas, such as diatomic hydrogen, is introduced into the chamber at a flow
rate preferably between 100 and 1,000 sccm and the pressure brought to
20-60 Torr. This hydrogen gas, when decomposed by a hot filament or
plasma, will react with and etch away the carbonized photoresist layer 3
within a few minutes time, leaving the diamond powder layer 5.
Referring to FIG. 1f, the building of diamond structures on the substrate 1
is shown. The diamond deposition process is generally shown in U.S. Pat.
No. 4,925,701 to Jansen et al. which is incorporated herein by reference
in its entirety. Briefly, a carbon containing gas or vapor such as
methane, ethane, ethylene, acetylene, ethanol, and the like is injected
with the hydrogen gas as mentioned in the description of FIG. 1 e. The
concentration of the carbon containing gas is preferably between 0.1 to 3
percent by volume than that of the hydrogen gas. The gas mixture is
brought to a total pressure of preferably between 20 and 60 Torr. The gas
mixture is decomposed in the deposition chamber by, for example, passing
the gas mixture over a hot filament having a temperature preferably
between 1800.degree.-2100.degree. C., or by the application of a microwave
plasma. This mixture can be brought in contact with the substrate 1. The
diamond powder layer 5, serves as a multitude of nucleation or seeding
areas, and thus, diamond growth occurs in only the patterned areas where
diamond powder remains on the surface of the substrate 1.
Other methods of decomposing gas mixtures in diamond deposition procedures
are well known to those skilled in the art, reference publication by S.
Matsumoto, Y. Sato, M. Tsutsumi, N. Setaka, J. Mat. Sci 17 (1982) 3106; by
M. Kamo, Y. Sato, S. Matsumoto, N. Setaka, J. Crystal Growth 62 (1983)
642; by H. Kawarada, K. S. Mar, A. Hiraki, Jpn. J. Appl. Phys. 26 (1987)L
1032; by K. Kurihara, K. Sasaki, M. Kawarada, N. Koshino, Appl. Phys.
Lett. 52 (1988) 437; and by M. Murakawa, S. Takeuchi, Y. Hirose, Surface
and Coatings Technology 39/40 (1989) 235, the disclosure of which are
totally incorporated herein by reference. These different methods for the
decomposition of gases all yield essentially the same end result and only
differ by the time period that is needed to deposit a film of a desired
thickness.
Another embodiment of the present invention is shown in FIGS. 2a-f. The
method of forming diamond structures on a substrate is similar to that
shown in FIGS. 1a-f. The methods differ as to when the diamond powder
layer is formed on the substrate. A substrate 1 is shown in FIG. 2a. The
substrate is then coated with photoresist to form photoresist layer 3 and
soft baked at 90.degree. for 15 minutes, as shown in FIG. 2b. A mask 7 is
placed over the photoresist layer 3, and the photoresist layer 3 is
exposed to electromagnetic radiation, such as Ultra-Violet light, through
the mask 7, for a period of time. Referring to FIG. 2c, a diamond powder
layer 5 is then added to the exposed photoresist layer 3. As seen in FIG.
2d, the photoresist layer 3 is then developed, thus removing parts of the
diamond powder layer 5 in areas where the photoresist layer 3 is
developed. The substrate is then placed in a processing apparatus, such as
a deposition chamber, and exposed to a high temperature which carbonizes
the photoresist layer 3. The substrate 1 is then exposed to a mixture of
hydrogen-containing and carbon-containing gases at a high temperature and
reduced pressure. The hydrogen-containing gas when decomposed by a hot
filament or microwave plasma etches away the carbonized photoresist layer
3. The combination of hydrogen and carbon-containing gases causes the
growth of diamond structures on the patterned diamond layer 5, as seen in
FIG. 2f.
Referring to FIG. 3, a scanning electron micrograph is shown. The scanning
electron microscope has been used throughout for measuring dimensions of
materials in the present invention. A diamond structure is shown having a
high resolution. The diamond structure can have a thickness as small as
0.1 microns and larger than 1000 microns. Several steps can be taken in
order to prevent diamond crystallization on the substrate in areas outside
of the pattern. First of all, performing the method of the present
invention in a clean room environment will prevent the deposition of
particulate matter onto the substrate. Particulate matter may form
nucleation centers for diamond crystallization. Also, it is important that
there are no abrasions on the substrate surface. Abrasions in the
substrate surface may also form nucleation centers for diamond
crystallization. Extraneous diamond crystals can be removed using a second
lift-off procedure. If the substrate 1 is made of silicon or a similar
material, a protective layer such as silicon nitride or silicon oxide can
be formed directly on the substrate I. This oxide or nitride layer is
formed on the surface of the substrate 1 in the developed areas of the
photoresist layer (See FIG. 1d). After diamond structures are formed on
the diamond powder layer 5 (See FIG. 1f), the oxide or nitride layer can
be removed, along with any extraneous diamond crystals, using any of a
variety of well-known methods.
A continuous diamond thin film can be formed over the substrate 1 using the
present invention. This is simply done by foregoing the exposing and
development steps mentioned above. After the diamond powder layer has been
formed on the photoresist layer, the photoresist layer is carbonized at a
high temperature and etched away during the diamond deposition process.
In further embodiments of the present invention, the diamond powder layer
can be incorporated in the photoresist layer. Also, the diamond powder
layer can be placed underneath the photoresist layer. After the
photoresist is developed, unwanted extraneous diamond particles can be
etched away in any of a variety of well-known methods.
The above is a detailed description of a particular embodiment of the
invention. The full scope of the invention is set out in the claims that
follow and their equivalents. Accordingly, the claims and specification
should not be construed to unduly narrow the full scope of protection to
which the invention is entitled.
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